I switched from using java to python for doing leetcode. Here are some of the tricks i discovered, I am hoping to learn more tricks from people here.

1. for - else

   • code block in else caluse executes when for finishes without break

2. itertools.accumulate

   • For prefix sums, prefix products ect.

3. tuple + @lru_cache

   • Sometimes you need to pass in a list as an agrument to method that you want to memoize, lists are mutable so convert list to tuple to make it memoizable.

4. enumerate

   • traverse list with its index

5. defaultdict

   • default values if key is missing from the dictionary

6. neighbors and bound checking in a matrix:

       for I, J in (i+1, j), (i-1, j), (i, j+1), (i, j-1):
         if 0 <= I < len(rooms) and 0 <= J < len(rooms[0]): continue
      

7. Instead of

     while Q:		 
       el = Q.pop_left()
       Q.append(x)

   do

    for el in Q:
      Q+=	x,   #  note the , in the end

8. Max fuction with key

   max([10,25,11,19], key= lambda x: x%10) 
   #19

9. mulitiple comparision operator

   a>10 and a<20
   10 <a <20

10. ~
~ : logical not inverts all bits in a number, useful for traversing a list in reverse.

      def is_palindrome(s):
         return all([s[i] == s[~i] for i in range(len(s)//2)])

I will keep updating this list if i can think of more or from comments here.

contributers : @user2708P

references:
https://leetcode.com/problems/walls-and-gates/discuss/72753/6-lines-O(mn)-Python-BFS

Thank you <3